Diversity, biological and molecular characterization of cucurbit viruses and disease epidemiology in Serbia

Abstract

In the period from 2007 to 2011 constant high levels of viral infections were detected in 61 cucurbit growing localities in Serbia. The frequency of viral infection fluctuated over the years, ranging from 30-50% in 2007, to the extremely high 80% in the epidemic year of 2008, while it was constant and around 40% in the next two years. In the last year of investigation, the frequency reached a very high level of 60%. Serological testing of 1100 collected samples proved the presence of three viruses: Zucchini yellow mosaic virus (ZYMV), Watermelon mosaic virus (WMV) and Cucumber mosaic virus (CMV). Additional testing of symptomatic samples revealed the presence of Cucurbit aphid-borne yellows virus (CABYV), which represents the first detection of CABYV in Serbia, and Tomato spotted wilt virus (TSWV), which is the first report of TSWV on cucurbits in Serbia and the first report of Cucurbita maxima as natural host plant worldwide. ZYMV was the most prevalent virus during this five year survey. Mixed infections were the most frequent infection type in the first two years, while single infection prevailed in the last three years of investigation. During this investigation, transmission of ZYMV by seeds of C. pepo var. styriaca, C. maxima and C. moschata was proved. Both annual and perennial weeds, which are present during the establishment of cucurbit crops, and in the beginning stages of vegetation, were infected with ZYMV, WMV, CMV and TSWV. The most prevalent was TSWV which was detected in eight different weed species, the second most prevalent virus in weeds was CMV, detected in seven different weed species, while the prevalence of ZYMV and WMV was similar and they were detected in five and four weed species, respectively. A high diversity of aphids which are visiting cucurbit crops was detected through the determination of 57 aphid taxons. The most common aphid species were Aphis fabae, Anoecia corni, Aphis gossypii, Myzus persicae and Acyrthosiphon pisum. The greatest diversity and the largest number of aphids were detected in the first few weeks after plant sprouting. The detection and identification of the species level for all five cucurbit viruses in Serbia were confirmed by RT-PCR method and suitable specific primers. Bioassay on 45 test plants was used to determine phenotypic variability and host range for ZYMV, WMV and CMV. During the course of this investigation protocols for molecular detection of all five cucurbit viruses in Serbia were established or improved. Molecular characterizations of ZYMV, WMV, CMV, TSWV and CABYV were conducted by sequence and phylogenetic analyses. Sequence analysis of the CP gene revealed that Serbian ZYMV isolates belong to the Central European group of isolates. Sequence analysis based on NIb and CP genes showed that Serbian WMV isolates are grouped in two groups, and one of them represents a group of "emerging" strains containing isolates which are known for causing severe damaging symptoms on cucurbits, and this represents the first report of these isolates in Serbia. Bas...

Diversity and flight activity of aphid species as potential vectors of oilseed pumpkin viruses in Serbia

“…The highest number of collected aphid species (maximum population density) in yellow traps was in Bački Petrovac locality in 2011, representing 28.3% of all collected species. In 2011 in the Vojvodina Province, the average estimated disease incidence was high, over 60%, ZYMV was the most prevalent virus, while CMV and WMV were also detected but in slightly lower percentage, and the number of mixed, including triple infections, was higher than the number of single infections (Vučurović, 2013). The most abundant species identified in 2011 were A. pisum and A. fabae.…”